In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years for a variety of applications including lighting and displays. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light or displays. Unfortunately, drawbacks exist with the conventional light bulb:                The conventional light bulb dissipates more than 90% of the energy used as thermal energy.        The conventional light bulb routinely fails due to thermal expansion and contraction of the filament element.        The conventional light bulb emits light over a broad spectrum, much of which is not perceived by the human eye.        The conventional light bulb emits in all directions, which is undesirable for applications requiring strong directionality or focus, e.g. projection displays, optical data storage, etc.        
To overcome some of the drawbacks of the conventional light bulb, fluorescent lighting has been developed. Fluorescent lighting uses an optically clear tube structure filled with a halogen gas and, which typically also contains mercury. A pair of electrodes is coupled between the halogen gas and couples to an alternating power source through a ballast. Once the gas has been excited, it discharges to emit light. Typically, the optically clear tube is coated with phosphors, which are excited by the light. Many building structures use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket.
Due to the high efficiency, long lifetimes, low cost, and non-toxicity offered by solid state lighting technology, light emitting diodes (LED) have rapidly emerged as the illumination technology of choice. An LED is a two-lead semiconductor light source typically based on a p-i-n junction diode, which emits electromagnetic radiation when activated. The emission from an LED is spontaneous and is typically in a Lambertian pattern. When a suitable voltage is applied to the leads, electrons and holes recombine within the device releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light is determined by the energy band gap of the semiconductor.
Appearing as practical electronic components in 1962 the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity, and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
The earliest blue and violet gallium nitride (GaN)-based LEDs were fabricated using a metal-insulator-semiconductor structure due to a lack of p-type GaN. The first p-n junction GaN LED was demonstrated by Amano et al. using the LEEBI treatment to obtain p-type GaN in 1989. They obtained the current-voltage (I-V) curve and electroluminescence of the LEDs, but did not record the output power or the efficiency of the LEDs. Nakamura et al. demonstrated the p-n junction GaN LED using the low-temperature GaN buffer and the LEEBI treatment in 1991 with an output power of 42 uW at 20 mA. The first p-GaN/n-InGaN/n-GaN DH blue LEDs were demonstrated by Nakamura et al. in 1993. The LED showed a strong band-edge emission of InGaN in a blue wavelength regime with an emission wavelength of 440 nm under a forward biased condition. The output power and the EQE were 125 uW and 0.22%, respectively, at a forward current of 20 mA. In 1994, Nakamura et al. demonstrated commercially available blue LEDs with an output power of 1.5 mW, an EQE of 2.7%, and the emission wavelength of 450 nm. On Oct. 7, 2014, the Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for “the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources” or, less formally, LED lamps.
By combining GaN-based LEDs with wavelength converting materials such as phosphors, solid-state white light sources were realized. This technology utilizing GaN-based LEDs and phosphor materials to produce white light is now illuminating the world around us as a result of the many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.
While LED-based light sources offer great advantages over incandescent based sources, there are still challenges and limitations associated with LED device physics. The first limitation is the so called “droop” phenomenon that plagues GaN based LEDs. The droop effect leads to power rollover with increased current density, which forces LEDs to hit peak external quantum efficiency at very low current densities in the 10-200 A/cm2 range. Thus, to maximize efficiency of the LED based light source, the current density must be limited to low values where the light output is also limited. The result is low output power per unit area of LED die [flux], which forces the use large LED die areas to meet the brightness requirements for most applications. For example, a typical LED based lightbulb will require 3 mm2 to 30 mm2 of epi area. A second limitation of LEDs is also related to their brightness, more specifically it is related to their spatial brightness. A conventional high brightness LED emits ˜1 W per mm2 of epi area. With some advances and breakthrough perhaps this can be increased up to 5-10× to 5-10 W per mm2 of epi area. Finally, LEDs fabricated on conventional c-plane GaN suffer from strong internal polarization fields, which spatially separate the electron and hole wave functions and lead to poor radiative recombination efficiency. Since this phenomenon becomes more pronounced in InGaN layers with increased indium content for increased wavelength emission, extending the performance of UV or blue GaN-based LEDs to the blue-green or green regime has been difficult.
Although useful, LEDs still have limitations that are desirable to overcome in accordance to the inventions described in the following disclosure.